Various "straight line" sealing machines for applying closures onto containers are disclosed in U.S. Pat. Nos. 3,143,835, 3,274,748, 3,438,174, 4,199,914, 4,279,115 and 4,716,708. These machines generally include a linear horizontal conveyor which carries filled open containers in a row sequentially through a closure feeding device, a closure applicator and a closure sealing means. The closure feeding device typically feeds or presents the closures to the moving containers via a chute or slide mechanism. As the containers are moved by the conveyor, the leading edge of a respective presented closure is engaged by the leading edge of the top of a respective container. The continuing movement of the container pulls the closure from its feed position so that it is seated on the container. Subsequently, means known per se press the closures onto the containers and/or rotate the closures onto the containers to seal the containers.
The maximum practical operating speed for previous machines of this type has been limited due to the nature of the closure feeding and application devices. When operated at desirable higher speeds, the reliability and accuracy with which the closures are engaged and seated upon the container tops is diminished. In particular, at very high speeds (for example, about 1,200 containers per minute) the impact of the leading edge of the container on the leading edge of the closure not only draws the closure from the feed position but may also "throw" or dislodge the closure so that the closure is not seated on the container whatsoever. Alternatively, the closure may end up "cocked" or improperly seated on the container as a result of which it cannot be properly sealed by the subsequent application and sealing means.
Other types of "straight line" sealing machines are disclosed in U.S. Pat. No. 3,392,505 and 4,696,143. The '505 patent is directed to a dual head apparatus for applying closures to containers. The disclosed apparatus includes a transfer head for removing closures from a dispenser and transferring them to an inserter head, which, in turn, applies the closures to containers. During the transferring step, the closures are each reoriented about a transverse axis so that they may be presented with their bottom side facing towards the opening of the containers to which they will be applied. The complexity of the closure pick-up and transfer mechanism of this machine does not lend itself to effective high-speed capping.
The '143 patent is directed to a container capping apparatus and includes a rotating carriage that receives the container caps from a conveyor and subsequently applies those caps to containers moving on a second conveyor. This machine is designed and operated such that the rotating carriage has a tangential velocity proximate the container conveyor that exceeds the linear velocity of the container conveyor, and thus the speed of the containers on the conveyor is wholly controlled by the rotating carriage at the location whereat the caps are applied to the containers. This machine is likewise not capable of effective high-speed capping.
What is needed is an improved sealing machine that can be operated at speeds heretofore not reliably attainable, while maintaining the integrity of the sealing operation with relatively few rejections.